Zeolite and other porous crystalline molecular sieve catalysts are increasingly being used in low temperature, liquid phase aromatic alkylation processes including ethylbenzene, cumene, and linear polyalkylbenzene (LAB) synthesis. Operation at lower temperatures improves process economics and, in many cases, product selectivity. However, trace feed impurities such as low molecular weight nitrogen, sulfur, and oxygen compounds, which are not strongly adsorbed in higher temperature vapor phase alkylation processes, are more problematic in the liquid phase processes. The affinity of these compounds for the active sites in the molecular sieve catalyst can cause rapid deactivation by displacing or neutralizing the acid site.
There are numerous methods known for reactivating catalysts. U.S. Pat. No. 2,541,044 to Daugherty discloses catalytic alkylation with simultaneous restoration of the alkylation catalyst activity by contacting the catalyst with an alkylatable hydrocarbon while interrupting the flow of alkylating agent. U.S. Pat. No. 3,148,155 to Schwartz describes removing metal poisons from cracking catalysts by contacting the poisoned catalyst with an aqueous solution of sulfurous acid, a water-soluble salt of sulfurous acid or a water-soluble salt of hyposulfurous acid. U.S. Pat. No. 4,418,235 to Haag discloses aromatic alkylation in the presence of steam to enhance or preserve zeolite catalyst activity. U.S. Pat. No. 4,550,090 to Degnan et al. describes a method for displacing high molecular weight poisons from ZSM-5 catalysts, such as those used in dewaxing, by in-situ treatment with more easily desorbed compounds such as ammonia or by treatment with alkali or alkaline metal cations to effect ion exchange. U.S. Pat. No. 4,276,149 to Chester et al. describes passivating metal contaminants on zeolite cracking catalysts by contacting with steam for limited periods. U.S. Pat. No. 4,678,764 to Le et al. discloses reactivation of noble metal-containing zeolites poisoned with sulfur oxides by contacting with aqueous acid solutions, e.g., nitric, carbon, acetic and formic acids. U.S. Pat. No. 4,319,057 to Kiser discloses regenerating molecular sieve dehydration materials with methanol or acetone. U.S. Pat. No. 5,425,934 to Malla et al. teaches treating zeolites with methanol, ethanol or propanol plus nitric or sulfuric acid for the removal of organic templates. U.S. Pat. Nos. 4,365,104 and 4,477,585 to Kaeding disclose enhancing para-selectivity of zeolite alkylation catalysts by treatment with hydrogen sulfide or carbon dioxide. U.S. Pat. No. 4,490,570 to Forward et al. discloses para-selective alkylation of a monoalkylbenzene wherein water in the form of steam can be co-fed with the reactants. U.S. Pat. No. 5,077,445 to Le discloses a process for liquid-phase synthesis of an alkylbenzene, such as ethylbenzene, using MCM-22 zeolite catalyst hydrated with liquid water. U.S. Pat. No. 5,191,135 to Dwyer et al. discloses preparing long chain alkyl substituted aromatic compounds by alkylating naphthalenes with C6+ alkylating agent in the presence of large pore size zeolite such as USY and MCM-22 in the presence of 0.5 to 3.0 wt % co-fed water to increase selectivity to monoalkyl-substituted products.
All of the above patents are incorporated in their entirety herein by reference.
It would be desirable to provide a process for reactivating liquid phase alkylation catalysts which have been contaminated by trace quantities of strongly sorbed poisons. It would be especially useful to provide a method for reactivating such catalysts in-situ by treatment with species that are introduced along with the liquid phase or vapor phase feed streams.